<template>
  <div>
    <router-link tag="div" to="/" class="header-abs" v-show="showAbs">
      <span class="iconfont header-abs-back">&#xe624;</span>
    </router-link>
    <div class="header-fixed" v-show="!showAbs" :style="opacityStyle">
      城市选择
      <router-link to="/">
        <span class="iconfont header-fixed-back">&#xe624;</span>
      </router-link>
    </div>
  </div>
</template>

<script>
export default {
  name: 'DetailHeader',
  data () {
    return {
      showAbs: true,
      opacityStyle: {
        opacity: 0
      }
    }
  },
  methods: {
    handleScroll () {
      const top = document.documentElement.scrollTop || window.pageYOffset || document.body.scrollTop
      if (top > 50) {
        let opacity = top / 140
        opacity = opacity > 1 ? 1 : opacity
        this.opacityStyle = {
          opacity
        }
        this.showAbs = false
      } else {
        this.showAbs = true
      }
    }
  },
  mounted () {
    window.addEventListener('scroll', this.handleScroll)
  },
  destroyed () {
    window.removeEventListener('scroll', this.handleScroll)
  }
}
</script>

<style lang="stylus" scoped>
@import "~styles/varibles.styl"
.header-abs
  position: absolute
  left: .2rem
  top: .2rem
  width .8rem
  height:.8rem
  line-height:.8rem
  border-radius .4rem
  text-align center
  background rgba(0,0,0,.8rem)
  .header-abs-back
    color #ffffff
    font-size: .4rem;
.header-fixed
  z-index: 2
  position: fixed
  top: 0
  right: 0
  left: 0
  height:$headerHeight
  line-height:.86rem
  text-align center
  color: #ffffff
  background $bgColor
  font-size: .3rem
  .header-fixed-back
    position: absolute
    left:0
    top:0
    width .64rem
    color #ffffff
    font-size: .4rem
</style>
